In recent years, from the prospect of depletion of oil resources in the future with a growing interest in the environment, it is more highly demanded than before to reduce fuel consumption in an automobile and a motorcycle, etc. On the other hand, there has been fast progress in the research and development of secondary cells represented by a lithium ion cell, and attempts to use electricity as a power source for driving the electric car or hybrid become popular.
Generally an electric motor has quite high energy efficiency compared with an internal-combustion engine, but it generates heat during its operation. A leading cause of the heat is generation of heat from a coil attributable to resistance of electrical currents flowing in windings (so-called copper loss). This causes a rise in the temperature of the coil, increasing the electrical resistance of the windings and lowering efficiency. The increased electrical resistance leads to generation of the heat again, falling in a vicious cycle of the generation of heat, the rise in temperature, and the increase in electrical resistance. This becomes an obstacle to improving output of a motor.
In addition, the generation of heat from an inverter (power supply circuit) for supplying electric power to an electric motor has also been a problem. Since a high voltage is applied to switching elements of the inverter and converter as well as to the coil of an electric motor, a large current flows also there. For this reason, it is required to efficiently deprive of the generated heat to cool these components.
For this reason, from the past, various cooling structures have been proposed to effectively cool the electric motor and inverter in an electric vehicle. For example, Patent Document 1 discloses the technology which water-cools a case of a motor and directly cools an exothermic portion of the motor using cooling oil, such as ATF, stored in the case. According to this technology, a coil wound around a core portion of a stator is resin-molded and an oil path for the cooling oil is provided near a coil end which is especially easy to rise to a high temperature.
A portion of windings of the coil end is exposed to this oil path, so that it is effectively cooled by the cooling oil. By supplying the cooling oil pumped up by a pump or the like to the oil path from above and squeezing out the cooling oil discharged from an outlet of a lower end of the oil path by shaping the outlet like an orifice, the whole oil path becomes filled with the cooling oil and the windings of the coil are immersed.
In addition, according to the cooling structure disclosed in Patent Document 2, a housing of a motor unit is cooled by a coolant (LLC), a storage part for an inverter and a smoothing capacitor as well as a storage part for an electric motor are provided in the housing, and a module of the inverter and capacitor accommodated in the accommodating portion is brought into contact with a metal-based cooler in which a coolant flows.
In addition, for example, Patent Document 3 discloses the motor configured such that a cooling oil, such as ATF and gear oil, is sprayed at an coil end of a stator so that the coil end can be cooled. According to this configuration, the cooling oil is sprayed onto the coil end of the stator in a manner that the cooling oil is first introduced into a hollow portion formed near an end plate of a rotor via an oil path in a shaft, and then the cooling oil is ejected from an ejection hole communicating with the hollow portion by a centrifugal force generated by revolution of the rotor.